1. Field of the Invention
The present invention relates to a reactive filtration apparatus and process for removal of living, suspended and soluble contaminants from liquid. Specifically, the filtration apparatus and process of this invention involves the use of reactive filtration media and at least one central flow control for contaminants removal and the ease of filter operation.
There are two types of conventional granular filters: slow sand filters and rapid sand filters. A typical conventional slow sand filter is commonly operated at below 0.16 gpm per square foot, using unstratified non-reactive sands with an effective size of 0.3 mm to 0.35 mm and a uniformity coefficient of 2 to 3. Aside from the low hydraulic load, conventional slow sand filters appear to lack the technological sophistication of their successors, conventional rapid sand filters which are operated at 2 gpm per square foot or higher, using stratified non-reactive sands with an effective size of 0.45 mm and higher and an uniformity coefficient of 1.5 or lower. Both types of conventional filters have operation and maintenance problems. Ordinarily the surface of a partially dewatered slow sand filter bed is raked after about 2 weeks of filter run, and again a week or so later to break through the surface accumulations. At the end of a month, the top portion up to 2 inches of the slow sand bed and the surface accumulations must be scraped off for disposal. Conventional rapid sand filters are superior to conventional slow sand filters for water filtration, but are comparatively more complicate, and can only be operated by experienced operators.
Furthermore, both conventional slow sand filters and conventional rapid sand filters remove only suspended particulates from water. Soluble contaminants, such as iron, manganese heavy metals, volatile organic compounds, and hardness can not be removed by any conventional sand filters.
Recently, the design of granular filters has been advanced to include granular activated carbons, activated alumina, anion exchange resins and cation ion exchange resins for removal of soluble contaminants. Other state-of-the-art processes for water purification include reverse osmosis, electrodialysis, packed column, ultrafiltration, microfiltration, diatomaceous earth filtration, flotation-filtration, etc. The common problems for the state-of-the-art as well as conventional filters are their high cost and time-consuming procedures for operation and regeneration.
The present invention adopts reactive granular filter media for specific liquid-solid separation, and adopts at least one central flow control for both regeneration of filter media and ease of routine operation. The present invention's apparatus is compact, and its process is simple and cost-effective, and can remove suspended, dissolved, volatile and living contaminants from liquid.
2. Description of the Prior Art
None of the prior arts including Barrows (U.S. Pat. No. 103280; 5/1870), Potter (U.S. Pat. No. 619838, 2/1899), Moon et al (U.S. Pat. No 2993599, 7/1961), Griswold (U.S. Pat. No. 3064816, 11/1962), Lindstol (U.S. Pat. No. 4082664, 4/1978), Litzenburger (U.S. Pat. No. 4430220, 2/1984), Hall et al (U.S. Pat. No. 4626346, 12/1986), Heskett (U.S. Pat. No. 4642192, 1987), Swinney et al (U.S. Pat. No 4673498, 6/1987), Krofta (U.S. Pat. No. 4377485, 3/1983; No. 4626345, 12/1986; 4673494, 6/1987), and Weber et al (U.S. Pat. No. 4973404, 11/1990) relate to the use of ultraviolet (UV) light, reactive granular filter media, chemical regeneration, central flow control, and crossflow hydraulic flow pattern in combination for water purification as in the case of this present invention.
In accordance with a recent publication by Wang & Wang (1989), conventional crossflow separation processes include reverse osmosis, ultrafiltration, microfiltration and gas permeation which are all membrane processes. The present invention relates to a central controlled crossflow granular reactive filtration process in which the filter media are regenerative with UV, ozone, hydrogen peroxide, hypochlorite, permanganate, and by which both living and non-living contaminants are efficiently removed under a pressurized rotating crossflow hydraulic condition for a prolonged filter run.
All conventional granular media filtration processes adapt either an upflow or a down-flow hydraulic operation during which the direction of influent flow is parallel with the flow path of granular media filtration. In the case of the present invention's crossflow granular reactive filtration process, the direction of influent flow is perpendicular to the flow path of granular media filtration.
Non-reactive granular filtration processes remove mainly suspended particulates from water. A reactive granular filtration process, as in the case of the present invention removes dissolve and living contaminants in addition to its capability for suspended particulates removal.
The major advantages of the present invention over conventional filtration processes include: (a) pretreatment and/or post-treatment of reactive granular filtration with ultraviolet (UV), ozonation, hydrogen peroxide, permanganate, and dry hypochlorite for total destruction of living contaminants; and (b) adoption of central flow control for the ease of nine granular reactive filtration operations: normal reactive filtration, backwash, bypass, flushing, chemical preparation, recirculation, rinse, precoat I, and precoat II. Both total destruction of living contaminants and simple one control operation make the present invention extremely attractive to the single families and small institutions for their point-of-entry (POE) in-house operations.
The similarities and dissimilarities between the present invention and the selected important prior arts are further described below.
British Patent No. 842, issued to Chemesha et al in March, 1870 is of interest in citing "safety valves", which are now required for any pressure systems including the present invention. While the safety valves and pipes are the required parts of the present invention, they are not considered to be major components of the present invention which places emphasis on a central controlled crossflow granular reactive filtration process.
All Krofta processes (U.S. Pat. Nos. 4,377,485, 4,626,345 and 4,673,494) are similar to a flotation-filtration system described by Wang (Oct., 1988). While the flotation-filtration process is feasible for removal of color, trihalomethane precursors and Giardia Cysts, the flotation-filtration process system involves the use of too many valves and treatment steps, and thus can only be adopted by municipalities which have skilled operators. The treatment steps of a flotation-filtration system include: chemical mixing, chemical flocculation, dissolved air flotation, non-reactive sand filtration, and chlorination, which are different from the present invention.
Filtration apparatus which adopt multi-port control values for feeding filter aids are shown in U.S. Pat. No. 3,064,816 issued Nov. 20, 1962 to David E. Griswold and in U.S. Pat. No. 4,973,404 issued Nov. 27, 1990 to Roland E. Weber, John J. Pavlovich and Lawrence K. Wang. Both filtration apparatus (U.S. Pat. Nos. 3,064,816 and 4,973,404) involve the use of too many valves and non-reactive and non-regenerative granular filter media, for removal of suspended contaminants. The present invention involves the use of only one or two central flow controls (depending upon the hydraulic capacities) and reactive/regenerative granular filter media for removing suspended, dissolved and living contaminants.
A prior filtration apparatus using multiport valves for cleaning of filters and delivering adequate pressure is described in U.S. Pat. No. 103,280, issued May 24, 1870 to Thomas Barrows. Barrows' patent is particularly directed to a non-reactive, non-regenerative pressure filter using several three-way valves. Although Barrows' apparatus can be operated horizontally or vertically, it is not a crossflow separation process in accordance with the state-of-the-art engineering definition. Currently only the membrane processes (reverse osmosis, microfiltration, ulrafiltration, and gas permeation) are designed and classified as crossflow separation processes in which the influent water (Qi) is fed to an inlet of said apparatus at one end traveling in parallel with the membrane filtration medium; its concentrate (Qe) is discharged in small volume at the opposite end; and the filter effluent (Qe=Qi-Qc) passing through the membrane filter medium is discharged from the second outlet also at the opposite end of said apparatus. The present invention relates to a crossflow granular filtration process and apparatus in which the granular filter media (instead of membrane filter medium) is reactive/regenerative (instead of non-reactive/non-regenerative), and one central flow control valve has nine operational modes (instead of several three-way valves).
Still another apparatus for filtering water through porous media is shown in U.S. Pat. No. 619,838, issued Feb. 21, 1899, to Zoroaster F. Potter. Specifically, Potter's patent relates to a filtration apparatus comprising a chemical process tank coupled to a chemical feed system, an old central flow control valve with a handle for dialing and handling limited water flows only, a pressure filter containing non-reactive/non-regenerative granular filter media, an influent inlet, product liquid discharge pipe, waste drain, many multiple on-off ports, all connected with a piping system which contains a plurality of safety valves. The process of the present invention relates to a pressurized crossflow filtration using reactive/regenerative granular filter media, and with UV, ozone, hydrogen peroxide and hypochlorite as pretreatment and/or post-treatment. The apparatus of the present invention comprises a process tank coupled to a feed system for pretreatment and filter media regeneration (instead of feeding chemical only as in the case of Potter's patent), a modern central flow control valve with nine process operational modes and handling both water flows and filter media slurry (instead of limited operational modes and handling only water flows), a pressure filter containing reactive/regenerative granular filter media (instead of non-reactive/non-regenerative granular filter media) and being operated in a rotating crossflow hydraulic pattern (instead of non-crossflow hydraulic pattern), an influent inlet, a product liquid discharge pipe and a waste drain, all connected with the modern central flow control valve (instead of all connected with a piping system). Besides, simplicity is the major improvement of the present invention, because there are not many multiple on-off valves.
Still another prior filtration apparatus for automatic flow control is shown in U.S. Pat. No. 2,993,599 issued Jul. 25, 1961 to John J. Moon and Harold M. Hawkins. Their patent discloses a new control technology for automation of a precoat filtration process involving the use of a cycle timer, air inlets, air vents, wash solvent lines, sluice solvent lines, a precoat mix tank, a pressure filter, a filter feed line, an effluent line, a wash recycle line, a wash vapor receiver, drains, a filter cake discharge line, a pressure pump, safety valves, pressure gauges, flow meters, over 20 flow control valves, and a turbidity monitor. The apparatus of the present invention also comprises a pressure filter, a filter feed line, an effluent line, a recycle line, drains, a pressure pump, pressure gauges, a flow meter, a safety valve, and a tank. However, in the case of the present invention, the major improvements are: one central flow control valve (instead of over 20 valves), one multi-purpose tank (instead of one single-purpose tank just for precoating), one pressure filter containing reactive/regenerative granular filter media (instead of non-reactive/non-regenerative granular filter media), being operated as rotating crossflow hydraulic pattern horizontally or vertically (instead of non-crossflow hydraulic pattern), and having adequate pretreatment and post-treatment for removal of living, non-living, suspended and dissolved contaminants (instead of having no pretreatment and post-treatment for removal of mainly non-living suspended contaminants), all aiming at simplicity in operation and high efficiency in water purification. In addition, the present invention's apparatus does not require complicated automation when applied to single families and small institutions because of its one central flow control operation. For higher flow municipal applications, the present invention is automated mechanically and electrically (instead of electronically as in the case of Moon et al) again because of its simple central flow control operation.
A method for treating fluid to remove undesirable constituents contained therein such as chlorine and nitrate constituents is disclosed in the U.S. Pat. No. 4,642,192, issued Feb. 10, 1987 to Don E. Heskett. Heskett's method includes passing fluid containing chlorine and nitrate through a bed of granular metal particulate matter, having favorable redox potentials relative to the redox potentials of the undesirable constituents so as to establish conditions for spontaneous oxidation and reduction reactions between the undesirable constituents and the metal particles. Heskett's method relates to water treatment using only the metal particles. The present invention relates to a central controlled filtration system with pretreatment and post-treatment, and the metal septum (instead of metal particles) is one of eleven filter media adapted by the crossflow pressure filter.